24
N.H. Gokhale et al. / Inorganica Chimica Acta 349 (2003) 23Á29
/
2. Experimental
rotating anode source, and a deep brown crystal of 8a
using a Stoe IPDS area detector diffractometer, in both
cases using graphite-monochromatised Mo Ka radia-
tion. Both crystals were cooled to 200 K. Both the
structures were solved by direct methods, and refined
against F2 (all data, anisotropic thermal parameters for
all non-H atoms and isotropic for H atoms), using the
SHELXTL software suite [8]. Crystal data and numerical
parameters for the structural refinements are summar-
ized in Table 2.
2.1. Materials
Benzyloxybenzilidene-pyridine-2-carboxamidrazone
(3), t-butylbenzylidine-pyridine-2-carboxamidrazone
(4), naphthylidine-pyridine-2-carboxamidrazone (5), p-
chlorothioloxy-benzylidine-pyridine-2-carboxamidra-
zone (6), 2-acetylpyridine-pyridine-2-carboxamidrazone
(7), 2-acetylthiophene-pyridine-2-carboxamidrazone (8)
were synthesized according to the procedures described
previously [6,7]. Single crystals of 6, suitable for X-ray
diffraction studies, were grown from methanol. Copper
chloride dihydrate was the product of Qualigens Ltd.
(India). Solvents used were distilled prior to their use.
2.5. In vitro antimalarial activity against P. falciparum
3D7 strain
P. falciparum 3D7 [9] cultures were maintained in
RPMI 1640 medium at 37 8C, 5% CO2 at 5% hemato-
crit. Synchronized ring stage cultures were prepared by
15% sorbitol synchronization and diluted to 1% para-
sitemia. A 50 ml of the culture was added per well to 96
well plates in triplicate. Stock solutions of the test
compounds, plus control drugs were prepared at a
concentration of 20 mg mlꢁ1 in DMSO. Compounds
were tested in threefold serial dilution series with
triplicate at each concentration in 96 well plates, the
highest concentration being 30 mg mlꢁ1. After 24 h
incubation [3H] hypoxanthine was added (0.2 mCi per
well) and the plates were incubated for further 24 h.
ED50 values were calculated from [3H] hypoxanthine
uptake as described previously [10].
2.2. Physical measurements
Elemental analyses were carried out in the Micro-
analytical Lab of University of Pune and at Butterworh
Laboratories Ltd., Teddington, UK. IR spectra were
recorded as KBr discs in the range of 4000Á
on a Mattson 3000 FTIR spectrophotometer. Electronic
spectra in the range 200Á1100 nm were recorded on a
Spectronic Genesys-2 machine. The EPR spectra were
recorded on a Varian E109 spectrometer at 300 K using
DPPH compound as a calibrant. The magnetic suscept-
ibilities of the copper complexes were measured at 300 K
on a Faraday balance having field strength of 7000 G.
Cyclic voltammetric measurements were made in DMF
solvent on a Bioanalytical System BAS CV-27 instru-
ment with an XY recorder using Pt disc as the working
electrode against SCE and Pt wire as an auxiliary
electrode. Tetraethyl ammonium perchlorate (TEAP)
was used as a supporting electrolyte
/
500 cmꢁ1
/
3. Results and discussion
The interaction of pyridine-2-carboxamidrazones
with copper chloride in 1:1 molar ratio in ethanol results
in the monomeric copper complexes in good yields and
purity as revealed from the microanalyses (Table 1).
2.3. Synthesis of copper(II) complexes
The copper complexes were synthesized according to
the method described earlier for complexes 3a, 7a and 8a
(Scheme 1) [5,6]. Typically, the pyridine-2-carboxami-
drazone ligand and copper chloride dihydrate were
reacted in 1:1 molar ratio in ethanol for 1 h under
reflux. After leaving the reaction mixture to cool, the
product obtained was collected by filtration and dried
under vacuum. The deep brown rectangular crystals of
the complex 8a suitable for single crystal X-ray diffrac-
tion studies were obtained upon recrystallizing the
compound from acetonitrile. The analytical data on
the copper complexes are summarized in Table 1.
3.1. Crystal structure of 6
The molecular structure of the ligand 6 with number-
ing scheme is shown in Fig. 1, while the selected bond
distances and angles are listed in Table 3. The bond
lengths indicate that within the central chain of the
molecule, the C(7)Ã
/
N(4) and C(6)Ã
/
N(3) linkages have
largely double bond character, comparable with those
found in previously reported structures [11]. The two
double bonds display E and Z stereoisomerism, respec-
tively, as would be expected in order to prevent the
unfavourable steric interactions between CÃ
/H bonds
and nitrogen lone pairs. The unit consisting of the
amidrazone chain and the pyridyl and phenyl rings are
largely planar, with the largest deviation observed for
2.4. X-ray crystallography of the ligand 6 and copper
complex 8a
N(2) and S(1) from the mean plane being 0.364(1) and
˚
Data were measured on a yellow crystal of 6 using a
Bruker SMART Apex CCD diffractometer with a
0.287(1) A, respectively. The torsion angle C(12)Ã
/
C(13)Ã
/
S(1)ÃC(14) is found to be 77.39(13)8, indicating
/
Gokhale, Nikhil H.
